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The paper shows the possibility to use hydrothermal nanosilica as a modifying additive to increase the strength of concrete based on portland cement. The technology of obtaining hydrothermal nanosilica in the form of sols and nanopowders by ultrafiltration membrane concentration and cryochemical vacuum sublimation is proposed. The results of increased strength of concrete under compression by the addition of hydrothermal nanosilica Sol are presented. The experiments were performed on highly mobile concretes (ST = 10-19 cm) on equal-moving mixtures with water-cement ratio W/C = 0.61-0.71 at a dose of SiO 2 2 wt.% and the rate of superplasticizer polycarboxylate 0.95±0.05 mas.% by cement. At the initial stage of hardening when the age is 1 day, the increase in the compressive strength of concrete reached 90-128% compared to the control sample. At the age of 28 days the increase in strength was 40%. High chemisorption activity of hydrothermal nanopowder with respect to Ca(OH) 2 was determined in the experiment with lime medium. This indicates that the amorphous nanoadditive SiO 2 , which has a high specific surface area, causes the formation of high-strength hydrates of calcium silicates in the cement (lime) medium as a result of the pozzolan reaction, and this causes an increase in the strength of concrete.For citation: Potapov V.V., Efimenko Y.V., Gorev D.S. Modification of concrete by hydrothermal nanosilica. Nanotehnologii v stroitel'stve Machine-readable information on CC-licenses (HTML-code) in metadata of the paperNanotechnologies in Construction: A Scientific Internet-Journal Нанотехнологии в строительстве: научный Интернет-журнал 2019; 11 (3): 248-265 http://nanobuild.ru info@nanobuild.ru 249 RESEARCH RESULTS OF THE LEADING SCIENTISTS • РЕЗУЛЬТАТЫ ИССЛЕДОВАНИЙ ВЕДУЩИХ УЧЕНЫХ Модифицирование бетона гидротермальным нанокремнеземом Авторы: Потапов Вадим Владимирович, Научно-исследовательский геотехнологический центр ДВО РАН; Россия, Петропавловск-Камчатский, главный научный сотрудник, vadim_p@inbox.ru; Ефименко Юрий Васильевич, Филиал «ЦНИИП Минстроя России» Дальневосточный научно-исследовательский, проектно-конструкторский и технологический институт по строительству, Россия, Владивосток; зам. руководителя Центра «Строительные материалы и технологии» ДальНИИС, efimenko_yu_v@mail.ru; Горев Денис Сергеевич, Научно-исследовательский геотехнологический центр ДВО РАН; Россия, Петропавловск-Камчатский, старший научный сотрудник, denis.goreff2015@yandex.ruРезюме: Показана возможность применения гидротермального нанокремнезема как модифицирующей добавки для повышения прочности бетона на основе портландцемента. Предложена технология получения гидротермального нанокремнезема в виде золей и нанопорошков с помощью ультрафильтрационного мембранного концентрирования и криохимической вакуумной сублимации. Приведены результаты повышения прочности бетона при сжатии вводом добавки золя гидротермального нанокремнезема. Эксперименты выполнены на высокоподвижных бетонах (ОК = 10-19 см) на равноподвижных смесях с водоцементным отно...

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The technological mode of obtaining amorphous SiO2 nanopowders based on hydrothermal solutions is proposed in this study. Polycondensation of orthosilicic acid as well as ultrafiltration membrane separation, and cryochemical vacuum sublimation were used. The characteristics of nanopowders were determined by tunneling electron microscopy, low-temperature nitrogen adsorption, X-ray diffraction, and small-angle X-ray scattering. The scheme allows to adjust density, particle diameters of nanopowders, specific surface area, as well as diameters, area and volume of the pore. Thus, the structure of nanopowders is regulated—the volume fraction of the packing of spherical particles in aggregates and agglomerates, the size of agglomerates, and the number of particles in agglomerates. The pour densities of the nanopowders depend on the SiO2 content in sols, which were 0.02 to 0.3 g/cm3. Nanoparticles specific surface area was brought to 500 m2/g by low temperature polycondensation. Nanoparticle aggregates specific pore volume (0.2–0.3 g/cm3) weakly depend on powders density. The volume fraction of the packing of SiO2 nanoparticles in aggregates was 0.6–0.7. Solid samples of compacted nanopowders had a compressive strength of up to 337 MPa. Possible applications of hydrothermal SiO2 nanopowders are considered.